Method of pickling



May 28, 1963 E. SHAY 3,091,558

METHOD OF PICKLING Original Filed 001:. 30, 1957 2 Sheets-Sheet 1 our air INVENTOR Eli Shay May 28, 1963 E. SHAY METHOD OF PICKLING 2 Sheets-Sheet 2 Original Filed Oct. 30, 1957 INVENTOR Eli Shay W H H H H United States Patent 3,091,558 METHOD OF PICKLING Eli Shay, Warren, Ohio, assignor to The Wean Engineer- Company, Inc., Warren, Ohio, a corporation of Original application Oct. 30, 1957, Ser. No. 693,369, new Patent No. 3,000,385, dated Sept. 19, 1961. Divided and this application Sept. 30, 1960, Ser. No. 59,531 .3 Claims. (Cl. 134-15) This invention relates to the cleaning of products of substantial length by passing them in a substantially continuous manner through a pickling tank.

This application is a division of my co-pending application Serial Number 693,369, filed October 30, 1957, now Patent No. 3,000,385

In the treatment and fabrication of many products of extended length, such as ferrous strip and wire products, for example, it is frequently necessary that the products be cleaned prior to performing a particular operation upon them. The cleaning process may be acid or alkaline and is generally known as pickling. Speaking by way of ilus- 'tration, hot rolled steel strip is ordinarily covered with mill scale of ferrous oxides resulting from its exposure to air at elevated temperatures. The scale must be removed prior to cold rolling to avoid inclusions of scale in the cold rolled strip. The strip is, therefore, passed through a tank containing an acid pickling solution. The problems of handling the strip at either end of the pickling tank, of

Welding coils to form a continuous strip before pickling,

and of cutting the strip into manageable lengths after pickling, may reduce the strip speed in the pickling tank below the usual opera-ting speed or require that the line be stopped momentarily. Despite such variations in speed and stops, the process is substantially a continuous one in which the product moves through the tank as an endless member approximating a predetermined speed.

It is necessary for efiicient operation to add acid and water continuously to the pickling bath to maintain a proper concentration of acid and iron in the bath for optimum removal of the mill scale from the product. Heretofore, acid and water have been added at a predetermined rate calculated from the average speed and width of strip passing through the pickling tank. Hourly or more frequent titrations have been necessary to check the acid concentration in the tank and to make fine adjustments in the .acid and water flow, in accord with the results of the titrations. Regular corrections in the rate of acid and water flow have been necessary, and it has generally been necessary to overcorrect for the purpose of reto-ring a proper balance. To provide against insuflicient pickling, an excess of acid has normally been carried resulting in a waste of acid and acid attacks on the product after removal of the scale. Regardless of the particular product being pickled, certain problems will usually be present in some degree. The flow of the pickling agent must be controlled to maintain a sufiicient concentration for complete pickling, while holding attacks on the metal to a minimum. The maintenance of optimum conditions in the pickling tank reduces the amount of waste product which must bedisposed of, and is highly desirable for this reason alone, the disposal of pickling waste being a major operating problem.

I provide means for continuously pickling a product comprising a pickling tank through which the product is passed, product measuring means to continuously measure the rate at which the product passes through the tank and control means to introduce a pickling agent into the tank at a rate proportional to the rate of passage of product through the tank. I prefer to provide product speed measuring means and means to indicate the product size where- 3,091,558 Patented May 28, 1963 by the product area rate of passage through the pickling tank may be determined. I prefer to provide product speed measuring means, pickling agent control means in connection therewith and pickling agent gauge means whereby the rate of flow of the pickling agent may be determined for further adjustment of said flow. I further preferably provide control means for a dilutent in operative connection with the pickling agent control means whereby the dilutent may be introduced into the pickling tank proportionally with the pickling agent.

Other details, objects, and advantages of the invention will become apparent as the following description of a present preferred embodiment thereof proceeds.

In the accompanying drawing, I have illustrated a present preferred embodiment of my invention in which FIGURE 1 is a diagrammatic view showing a portion of a pickling tank with the associated controls being shown diagrammatically, and

FIGURE 2 is a side view of the exit end of acon-ventional pickle line embodying the invention, showing a portion of the pickling tank, the pinch rolls which pull strip through the pickling line and the strip washing and drying apparatus positioned between the pickling tank and pinch rolls.

In the accompanying drawing, a pickling tank is illustrated which is suitable for acid pickling of hot rolled strip prior to cold rolling. The handling of such strip is generally well-known. A particular type of installation is shown, for example, in United States Patent 2,196,600 to Raymond J. Wean and Donald A. McArthur. A portion of a pickling tank 1 is shown diagrammatically. The strip passes into the pickling tank at irregular speeds because of normal operating conditions. The strip is pulled from the tank between a pair of conventional pinch rolls in a continuous operation, although the speed varies widely, and the strip may even be stopped at times. One of the pinch rolls is illustrated at 2 and has a tachometer generator connected to it. The pinch roll is continuously in contact with the strip whereby it and the connected generator will rotate at a speed proportional to the strip speed, producing a proportional elect-ric' signal. The signal is transmitted on wires 4 to a transmitter 5 which will deliver-air to a pipe 6 at a pressure proportional to the generated voltage. A Foxboro E.M.F./pneumatic transmitter is a satisfactory instrument for this purpose. LA. manually set valve 7 supplies a regulated amount of air to a pipe 8. The valve supplies air at a reduced pressure which is proportional to the opening of the valve, and is calibrated in inches of strip width. Thus, by appropriate setting of valve 7, an air pressure in pipey8 is maintained which is proportional to the strip width. A Foxboro pneumatic airdron type 20 supply regulator is suitable at this point. A multiplier 9 multiplies the pressures in pipes 6 and 8 and transmits a resultant pressure in pipe .10. Consequently, the pressure in pipe 10 will be proportional to the area of strip passing through and leaving the pickling tank. A Foxboro M/40 black box computer is a satisfactory instrument for these purposes. A recorder '11 of conventional design continuously records the pressures in pipes 6 and "8 on a chart to make a permanent record, as well as to give visual indication of the pressures at any moment.

Sulfuric acid used for pickling is maintained in a head tank 12 and feeds through a supply pipe 13 into the pickling tank at a discharge point 14. Pipe 10 leads to a controller 15 which transmits the pressure through the pipe 16 to valve 17 in acid supply pipe 13. Valve '17 opens an amount proportional to the air pressure in pipe 16, thereby allowing acid to pass into the pickling tank in an amount proportional to the area of strip then passing into the pickling tank. A Foxboro stabilfio wide range controlvalve is suitable for this purpose. A solenoid valve .19 is normally maintained in open position but may be operated to close pipe 16, thereby stopping acid flow into the tank. It will be apparent that small variations in the acid flow may occur due to variations of level in head tank 1 2,v inaccuracies in valve and instrument settings, and the like. A- magnetic flow meter 20, such as that employed in a Foxboro magnetic flow control meter system, is placed in acid supply pipe 13. The flow meter measures the rate of flow of acid in supply pipe 13 and transmits a proportional electrical signal through wires 21. to a controller 15 such as a Foxboro dynalog electronic indicating controller transmitter with stabilog control mechanism, Model No. 96534448. By-pass valves 18' are provided around valve 17 and flow meter 20 for manual and emergency operation.

Controller 15 is responsive to the voltage in wires 21. It thenmodulatesthe pressure in pipe 16 to maintain an accurate flow in supply pipe 13 which is proportional to the pressure in pipe 1 1. This feedback serves to check the actual acid input continuously and to match it accurately to the signal indicating the rate of strip passage through tank 1. Controller 15 also records the actual flow of acid in supply pipe 13 on a chart and transmits in pipe 22 a pressure proportional to the actual flow of acid in the supply pipe 13. A dial type recorder 23 such as a Foxboro integrating recorder maintains a record of the total amount of acid discharged into tank 1.

A proportioning controller 24 is connected to pipe 22 and delivers a controlled air pressure in pipe 25 which is proportional'to the pressure in pipe 22. The ratio or pro portion may be manually set on controller 24. A Foxboro recording receiver ratio controllerflype M/40' stabilog is suitable for this purpose. iAir pressure in pipe 25 opens a pneumatic valve 26 proportionally, thereby discharging water through pipe 27 intothe pickling tank at discharge point 28. A flow meter 29 connected across an orifice -30 records'the actual flow of water in pipe 27. Manual by-passes 31 are provided around the valve 26 and orifice 30. The flow meter develops an air pressure in pipe 32 proportional tothe actual flow of water through orifice 30. Pipe 32 connects to a proportioning controller 34 such as a Foxboro indicating flow transmitter and serves as a feedbackfrom which controller 24 further adjusts valve 26' to maintain a correct flow of water in pipe 27. A dial type recorder 3 3, such as a Foxboro pneumatic receiver integrator, records the total gallons of water discharged into the pickling tank. Two pens in controller 24 continuously record the flow of acid and of water into pickling tank- 1.

From the foregoing, it will be apparent that the area of strip passing through the pickling tank is constantly being' determined and that acid is delivered to the pickling tank in a fixed proportion thereto. The actual flow of acid is measured, and this information is fed back to the controller for further precise adjustment of the acid flow control valve. In like manner, water is supplied to the pickling tank in an amount proportional to the acid flow. Similarly, the actual water flow is measured and fed back to the water flow controller for further adjustment of the water flow control valve. The acid-water ratio is adjusted manually to suit the particular operating conditions. Once set, this ratio is ordinarily maintained constant for given operating conditions, and future adjustments are made only infrequently. The amount of acid supplied may be cut off or increased through manual control to meet abnormal operating conditions or make corrections in the acid concentration if necessary. It has been found that the desired acid concentration is maintained much more closely than is possible with manual control. The time between titrations of the pickling tank solution has been increased, thereby reducing the labor required. Overly strong acid solutions are avoided, thereby making more effective use of the acid and minimizing acid attack on the product. It will be apparent that use of the invention is not limited to wide thin strip or any other product, that it may be used with products of other types and cross sections, such as wire, for example, and that any desired pickling agent may be employed.

While I have illustrated and described a present preferred embodiment of my invention, it is to be understood that I do not limit myself thereto and that the invention may be otherwise variously practiced within the scope of the following claims.

I claim:

1. The method of pickling a product of great length which passes. continuously through a pickling tank at variable speeds, which method comprises measuring the rate at which the product passes through the tank, determining therefrom the area rate of passage of product through the tank, and continuously discharging into-the tank a pickling agent in amounts proportional to the area rate of passage of product through the tank.

2. The method. of pickling a ferrous product of substantial length which is passed into a pickling tank at varying speeds which comprises continuously measuring the speed of passage of the ferrous product through the tank, determining therefrom the area rate of product passing through the tank, discharging an acid into the tank proportionally to the area rate of passage of ferrous product, and discharging water into the tank proportionally to the rate of introduction of acid.

3. The method of pickling a product of substantial length which is passed intoa pickling tank at varying speeds which comprises continuously measuring the speed of passage of the product through the tank, determining therefrom the area rate of product passing through the tank, discharging an alkali into the tank proportionally tothe' area rate of passage of said product, and discharging Water into the tank-proportionally to the rate of introduction of alkali.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF PICKLING A PRODUCT OF GREAT LENGTH WHICH PASSES CONTINUOUSLY THROUGH A PICKLING TANK AT VARIABLE SPEEDS, WHICH METHOD COMPRISES MEASURING THE RATE AT WHICH THE PRODUCT PASSES THROUGH THE TANK, DETERMINING THEREFROM THE AREA RATE OF PASSAGE OF PRODUCT THROUGH THE 